Solve this IQ quiz
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I would slightly modify your answer.Originally posted by geodome:1. Pick any 4 coins and put 2 on each side of the balance
2. Repeat Step 1 until the weight balancing device is no longer in balance.
3. one of the 4 coins that were placed on the balance last is the fake coin.
4. take one of these 4 coins and weigh it against one of the remainder coins.
Divide the coins into 3 groups of 4: A, B and C.
Compare A to B and A to C.
You will determine that the fake coin is in one these groups.
Of the four coins (w,x,y,z), select 2 and balance them
Then there would be 4 scenarios:
w and x balance, replace x with y, w balances with y, z is fake
w and x balance, replace x with y, w does not balance with y, y is fake
w and x does not blance, replace x with y, w balances with y, x is fake
w and x does not blance, replace x with y, w does not balances with y, w is fake
Total weighing :4 -
i very blur lao...Originally posted by tIfosI:I would slightly modify your answer.
Divide the coins into 3 groups of 4: A, B and C.
Compare A to B and A to C.
You will determine that the fake coin is in one these groups.
Of the four coins (w,x,y,z), select 2 and balance them
Then there would be 4 scenarios:
w and x balance, replace x with y, w balances with y, z is fake
w and x balance, replace x with y, w does not balance with y, y is fake
w and x does not blance, replace x with y, w balances with y, x is fake
w and x does not blance, replace x with y, w does not balances with y, w is fake
Total weighing :4 -
Answer edited - Initially I did it for 16 coins and managed to solve all within 4 steps, but sadly I erased my answer anyway.
Anyway here's my solution:
Split it into 3 groups, A, B, C.
*Let's say that the coin comes from Group C, thus A & B can be swapped interchangably.
Weight any 2 groups,
1)Weight A+B, if it's balanced, the coin is from group C.
Take 2 coins from group C and compare it with 2 real coins.
a)If it's still balanced, one of the other 2 coins is the fake one. Take one of the remaining 2 coins and weight it with a real coin.
If it's balanced the last coin is the fake one. If not, the coin which you just put onto the scale is fake.
b)If it's not balanced, then one of those 2 coins are fake. You are able to see if the fake coin is heavier or lighter. Further weigh those two coins and you'll be able to tell which one it is.
2a) Weight A+C, if it's not balanced, the fake coin comes from either group. Replace group A with B, if it's still not balanced, the coin comes from group C. You are able to see if the fake coin is lighter or heavier. Split the coins in group C into groups of 2, and weigh them. Since you already know if the coin is heavier or lighter, you can tell which group of 2 it comes from. Further weigh the two and you'll be able to find the fake coin.
2b) Weigh A+C, if it's not balanced, the fake coin comes from either group. Replace group C with group B, if it's balanced, the coin comes from the group you've just removed. You are able to see if the fake coin is heavier or lighter from your previous reading. Split the coins in group C into groups of 2, and weigh them. Since you already know if the coin is heavier or lighter, you can tell which group of 2 it comes from. Further weigh the two and you'll be able to find the fake coin.
Best case scenario - 3 steps
Worst case scenario - 4 steps
All scenarios covered. -
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Wait a minute....his solution is correct.Originally posted by BufPuf:wa lao eh
yrs damn complicated leh
mine answer is the best liao i think..hahahahaha
http://www.folj.com/puzzles/very-difficult-analytical-puzzles.htm
Cheat!
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my sentiments exactly.Originally posted by BufPuf:3 times
first time - 6 on each side..
second time - 3 on each side
3rd time, just choose any 2 to weigh. If they are the same, the other coin will be the lighter 1..
this isn't hard. i did it mentally in < 30s ;p give harder ones leh -
well you don't know if it's heavier or lighter.Originally posted by jenn_y:my sentiments exactly.
this isn't hard. i did it mentally in < 30s ;p give harder ones leh -
oh, oops guess i missed that lol.Originally posted by JennTS:well you don't know if it's heavier or lighter.